Method of controlling a wind power installation

ABSTRACT

A method for controlling a wind power installation at very high wind speeds, in which there is predetermined a first wind speed at which the rotor blades of the wind power installation are put into a first predetermined setting. In addition, the method includes controlling the wind power installation during an extreme wind situation where the rotor blades moved to a position to reduce, as far as possible, mechanical loadings on the wind power installation caused by the extreme wind situation.

TECHNICAL FIELD

The present invention concerns a method of controlling a wind powerinstallation at very high wind speeds, in which there is predetermined afirst wind speed at which the rotor blades of the wind powerinstallation are put into a first predetermined setting. The presentinvention further concerns a wind power installation, in particular forcarrying out such a control method, comprising an azimuth drive and arotor with at least one individually adjustable rotor blade.

BACKGROUND OF THE INVENTION

One method of controlling a wind power installation is described in DE195 32 409. Another method of controlling a wind power installation athigh wind speeds is described in Erich Hau, ‘Windkraftanlagen’ [‘Windpower installations’], Springer Verlag, 2nd edition, 1996, pages 89 ffand 235 ff.

That known state of the art predominantly describes measures which areadopted to protect wind power installations from overloading, at veryhigh wind speeds. In that respect, in particular mechanical loadings aretaken into consideration in order to avoid damage to the installationand/or individual components.

The standard measure described is usually putting the rotor blades intoa so-called feathered position. It will be noted however that anecessary condition for that purpose is that there is a possibility ofvarying the angle of attack of the rotor blades-so-called pitchadjustment. If such a possibility does not exist, a flow breakdown orstall condition is brought about at the rotor blades in order toimplement a relief of the load on the wind power installation.

A disadvantage with those known methods however is that no measures arespecified for wind speeds which continue to rise, above the firstpredetermined wind speed, so that it is only possible to trust that theinstallations are adequately dimensioned to prevent complete destructionof the installation and unavoidable acute endangerment, which this wouldinvolve, to the relatively close area around the installation.

SUMMARY OF THE INVENTION

Therefore one object of the present invention is to provide a method ofcontrolling a wind power installation and a wind power installation forcarrying out that method, which in an extreme wind situation are in aposition to reduce as far as possible mechanical loadings on the windpower installation, which occur due to that extreme wind.

To attain that object, the method of the kind set forth in the openingpart of this specification for controlling a wind power installation isdeveloped in such a way that upon the attainment of a secondpredetermined wind speed the machine housing is put into apredeterminable azimuth position. In that way it becomes possible forthe action taken to protect the wind power installation by suitableadjustment of the rotor blades, to be supported by adjustment of therotor into a position in which the wind resistance is particularly low.

In a preferred embodiment of the invention the rotor is rotated toleeward by adjustment of the azimuth position so that it is on the sideof the pylon of the wind power installation, which is remote from thewind.

In a particularly preferred embodiment of the method, besides theazimuth positioning of the machine housing and therewith the leewardorientation of the rotor the angle of attack of the adjustable rotorblades is so adjusted that they represent the lowest possible level ofresistance for the wind. In that way the loading on the entire windpower installation can be markedly reduced. For that purpose the rotorblades are in turn moved into the feathered position.

Particularly preferably the control according to the invention can besuch that in particular the loadings at one or more rotor blades aredetected. Such detection can be effected for example by ascertaining thewind speed at the rotor blade, the deformation of the rotor blade and/orother suitable ways (measurement of the tensile and compression forcesat the rotor blade or the rotor hub).

In a preferred development of the invention the twisting of cables whichextend in particular from the machine housing into the pylon, orvice-versa, is taken into account when establishing the direction ofmovement for adjustment of the azimuth position of the machine housing.In that way avoidable damage can actually be avoided. The firstpredetermined wind speed of the order of magnitude of about 20 m/s isalso usually referred to as the shut-down speed or limit speed. At thatspeed or a value somewhat thereabove, for example 25 m/s wind speed,most wind power installations shut down, that is to say, the entirerotor is braked and then no further power generation takes place.

In a particularly preferred development of the method the azimuth brakeand/or the rotor brake are released so that the wind blowing against theinstallation adjusts the leeward rotor automatically into the positionwith the lowest wind resistance, while at the same time the forces atthe rotor blades themselves can be reduced by possible rotation of therotor so that the method according to the invention provides that thewind power installation is adjusted in such a way that it can escape theforces of the wind as far as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantageous embodiments of the invention are characterized bythe appendant claims.

An embodiment by way of example of the invention is described in greaterdetail hereinafter with reference to the drawings in which:

FIG. 1 shows a wind power installation in normal operation,

FIG. 2 shows a wind power installation which has been adjusted by themethod according to the invention after a first wind speed is reached,and

FIG. 3 shows a wind power installation which has been adjusted by themethod according to the invention upon the attainment of a secondpredetermined wind speed.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a wind power installation which is in the form of awindward rotor—that is to say the rotor is at the side of the pylon 10,which is towards the wind. Disposed at the tip of the pylon 10 is themachine housing 12 with the generator (not shown) and the rotor blades14.

In this Figure this wind power installation shown by way of example isillustrated in normal operation and the rotor blades 14 are so adjustedthat they take the maximum power from the wind which is indicated by anarrow 20 to convert it into electrical energy.

FIG. 2 also shows a wind power installation with a pylon 10, at the tipof which there is a machine housing 12. This Figure shows a possiblesetting of the rotor blades 14 which is brought about by the control 13in accordance with the invention when a first predetermined wind speed,for example 20 m/s, is reached or exceeded. The control 13 may includeat least one microprocessor 15. The wind loads on the rotor blades 14are detected by wind load detector 17 located in the rotor side ofmachine housing 12. The rotor blades 14 are rotated into a so-calledfeathered position in which they are so oriented that they involve thelowest level of wind resistance when the wind speed exceeds a firstthreshold value.

In that way the loading which the wind 20 blowing against theinstallation exerts on the wind power installation 10, 12, 14 by way ofthe rotor blades 14 is markedly reduced. In addition in this positionthe flow naturally does not bear against the rotor blades 14 so that thecorresponding (lift) forces are also not produced. Accordingly no rotorrotation occurs.

In the case of wind power installations in which a variation in theangle of attack of the rotor blades 14 is not possible, a reaction onthe part of the control 13 corresponding to the method in accordancewith the invention can be, for example, a part of the rotor blade,preferably an outer part which is as far as possible from the rotor hub(not shown) is adjusted in such a way that the flow at the rotor bladesbreaks down and thus rotation is stopped.

In that condition however the forces acting on the rotor blades 14, themachine housing 12 and the pylon 10 are always still relatively greatand in particular the azimuth adjustment arrangement has to withstandconsiderable loadings.

In order to avoid damage the control 13 according to the inventiontherefore adjusts the azimuth position of the machine housing 12 uponthe attainment of a second predetermined wind speed of for example morethan 30 m/s–50 m/s, in such a way that the rotor is to leeward, that isto say at the side of the pylon 10, which is remote from the wind. Thisis shown in FIG. 3. The second predetermined wind speed is of an orderof magnitude such that reference can be made to a gale-force storm or ahurricane. At such wind speeds there is usually nothing moving onpreviously known wind power installations because both the azimuth brakeand also the rotor brake provide for complete stoppage of theinstallation.

In FIG. 3 the machine housing 12 at the tip of the pylon is sopositioned that the wind 20 firstly flows past the pylon 10 and onlythen reaches the rotor with the rotor blades 14. By virtue of releasingthe azimuth brake and the rotor brake, it becomes possible in thatcondition that the forces which arise out of the afflux flow of wind andwhich act in particular on the rotor blades 14 can result in freerotational movement of the machine housing 12 in the azimuth mounting sothat the wind ‘entrains’ the machine housing 12 upon changes in winddirection.

As can be seen from FIG. 3 the position of the rotor blades 14 hasremained unchanged in relation to the wind, that is to say the rotorblades 14 are still in the so-called feathered position in which theyoffer the lowest wind resistance.

As however the machine housing 12 of the wind power installation 10, 12,14 has been rotated from the windward position into the leewardposition, that is to say it has performed a rotary movement through180°, the rotor blades 14 are also rotated through 180° so that they canretain their position relative to the wind.

Accordingly the rotor blade mounting and the rotor blade drive areconstructed to allow such rotary movement.

In this respect, two basic methods and naturally any intermediatevariant are possible for varying the position of the rotor blades 14.One possibility provides firstly altering the azimuth position of themachine housing 12 in such a way that the rotor moves from windward toleeward and leaving the position of the rotor blades 14 unchanged duringthat adjusting movement. The result of this however is that, after arotary movement of about 90°, the rotor blades 14 are disposedtransversely with respect to the wind with their entire surface area,and thus offer the wind the full area to act thereon. Here release ofthe rotor brake can only limitedly afford a remedy as at least twoblades of which one is above the horizontal axis of the rotor and theother is below that axis are acted upon by the wind.

The preferred alternative involves retaining the position of the rotorblades 14 relative to the wind by a continuous change in the position ofthe rotor blades 14 relative to the wind by virtue of a continuouschange in the position of the rotor blades 14 with respect to themachine housing 12 (with the orientation relative to the wind remainingthe same) during adjustment of the azimuth position. Thus even in aposition of the machine housing 12 transversely with respect to the winddirection 20 the rotor blades 14 are in a feathered position and thusstill offer the lowest possible resistance when the wind speed exceeds asecond threshold value.

The above-described invention is suitable in particular for wind powerinstallations in an off-shore situation. As it is precisely in off-shoreoperations, that is to say in the case of wind power installations atthe open sea, the expectation is that they are in part exposed to thestrongest storms, but at the same time even in the event of minor damageto the installations they can be repaired substantially immediately, theinvention ensures that major or minor damage to the parts of theinstallation simply cannot occur because the adjustment of the rotorblades into the feathered position and the adjustment of the machinehousing into the leeward position provides that the wind loading on thewhole of the wind power installation and the parts thereof (inparticular the pylon) is as low as possible.

1. A method of controlling a wind power installation including a pylon,a machine housing and a rotor with rotor blades, the method comprising:moving the rotor blades of the wind power installation into a firstposition with respect to the machine housing when wind speed is above afirst predetermined value which is greater than 20 m/s; when wind speedis above a second predetermined value, allowing the wind to move themachine housing into an azimuth position such that the rotor and rotorblades are down wind from a rear end of the machine housing and from thepylon; and adjusting the rotor blades' position such that their positionwith respect to the main wind direction remains substantially unchangedafter the machine housing has moved into a down wind position from theirposition with respect to the main wind direction in their firstposition.
 2. The method according to claim 1 wherein the first positionof the rotor blades is a feather position to present low resistance towind.
 3. The method according to claim 1 wherein the rotor bladesmaintain the first position with respect to the machine housing as themachine housing is moved into the azimuth position.
 4. The methodaccording to claim 1 further comprising moving the rotor blades into asecond position with respect to the machine housing as the machinehousing is moved into the azimuth position, such that the rotor bladesretain a position substantially unchanged relative to wind directionduring the movement of the machine housing.
 5. The method according toclaim 4 wherein the second position of the rotor blades with respect tothe machine housing is a feather position to present low resistance tothe wind.
 6. The method of claim 4, further comprising preventing therotor from rotating when the rotor blades and the machine housing aremoving.
 7. The method of claim 4, wherein the moving the rotor bladesinto a first position, the moving the rotor blades into a secondposition, and the allowing the wind to move the machine housing into anazimuth position is controlled by at least one microprocessor in acontrol.
 8. The method according to claim 1 further comprising detectingwind loads on the rotor blades at the rotor.
 9. The method according toclaim 1 wherein the azimuth position of the machine housing places therotor in a leeward position relative to wind direction.
 10. A method ofoperating a wind power installation including a housing having one ormore blades mounted thereon, the method comprising: rotating the one ormore blades to feather the one or more blades if wind speed exceeds afirst threshold value while the housing is in a first position; rotatingthe housing to a second, low wind profile position if the wind speedexceeds a second threshold value and rotating the one or more blades toa second position to place the one or more blades in a featheredposition in the low wind profile position; and adjusting the rotorblades position in such a way that their position with respect to themain wind direction after rotating the housing remains substantiallyunchanged from their position with respect to the main wind directionwhen the housing was in the first position.
 11. The method according toclaim 10 wherein rotating the housing is carried out by turning thehousing to have the blades on a downwind side of the housing.
 12. Themethod of claim 10 in which the second threshold is higher than thefirst threshold.
 13. A method of controlling a wind power installationcomprising: placing rotator blades of the wind power installation into afeathered position so that a rotational speed of the rotator blades isreduced when a wind speed exceeds a first threshold; rotating a machinehousing to which the rotator blades are connected into a position havinga low wind profile position upon the wind speed being a second, higherpredetermined speed above a second threshold higher than the firstthreshold; and during the rotating of the machine housing to the lowwind profile position, rotating the rotator blades such that the rotatorblades remain in a feathered position with respect to wind direction.